Fix loaders option notation occurrences on README

Some examples was using the option loader for an array of loaders, 
but the option should be on plural when its value is an array.

Author: brnrdog

README.md

@@ -39,8 +39,8 @@ module.exports = {
   module: {
     loaders: [
       {
-        test:   /\.css$/,
-        loader: [
+        test: /\.css$/,
+        loaders: [
           'style-loader',
           'css-loader?importLoaders=1',
           'postcss-loader'
@@ -110,7 +110,7 @@ module.exports = {
     loaders: [
       {
         test:   /\.css$/,
-        loader: [
+        loaders: [
           'style-loader',
           'css-loader?importLoaders=1',
           'postcss-loader'
@@ -166,7 +166,7 @@ module.exports = {
     loaders: [
       {
         test:   /\.sss/,
-        loader: [
+        loaders: [
           'style-loader',
           'css-loader?importLoaders=1',
           'postcss-loader?parser=sugarss'
@@ -190,7 +190,7 @@ module.exports = {
     loaders: [
       {
         test: '\/.css',
-        loader: [
+        loaders: [
           'style-loader',
           'css-loader?importLoaders=1',
           'postcss-loader?sourceMap=inline'
@@ -213,7 +213,7 @@ either add the css-loader’s [`importLoaders`] option
 …
       {
         test: /\.css$/,
-        loader: [
+        loaders: [
           'style-loader',
           'css-loader?modules&importLoaders=1',
           'postcss-loader'
@@ -238,7 +238,7 @@ you can use the [postcss-js] parser.
 …
       {
         test: /\.style.js$/,
-        loader: [
+        loaders: [
           'style-loader',
           'css-loader?modules&importLoaders=1',
           'postcss-loader?parser=postcss-js',
@@ -270,7 +270,7 @@ If you use JS styles without `postcss-js` parser, you can add `exec` parameter:
 …
       {
         test:   /\.style.xyz$/,
-        loader: [
+        loaders: [
           'style-loader',
           'css-loader?modules&importLoaders=1',
           'postcss-loader?parser=custom-parser&exec'